X-ray tube safety device



Oct. 23, 1951 E. R. GOLDFIELD ETAL 2,572,258

X-RAY TUBE SAFETY DEVICE Filed July 20, 1946 2 SI-lEETS-SI-IEET 1 L E Y INVENTORS EDWIN R. GOLDFELD & JACK BALL BY WW 46% ATTORNEYS Oc 3, 1 51 E. R. GOLDFIELD ET AL 7 X-RAY TUBE SAFETY DEVICE Filed July 20, 1946 2 SHEETS-'-SHEET 2 LI l 9 u L r- E 22a 22b ""7 I 22 I2 INVENTORS EDWIN R. GOLDFIELD & JACK BALL BY i M ATTORN EYS Patented Oct. 23, 1951 UNITED STATES PATETN T OF FREE 7 572,258 XLRAY SAFETY DEVICE Edwin E. Golflfield, University neigm ana Jack Ball;- Cleveland"; Ohio, assignorsto Picker X-Ray Cor 'l'ora't'ion.Waite ManufacturingDiv'ision,-. Inc., Cleveland, Ohio, a corporation of Ohio spit-saith July 20, 1946, Serial No. 685,095

This invention relates to improvements in con trol; circuits for X-ray tubes and more particularly to improvements insafety devices -for preventing injury to X-raytubes by overloading thesame. I object of the present invention is" to provide; means for preventing arr-overly long exposure combined-with an excessive kilovoltage applied tothe tube'. w

Another object of the present invention is prevent an excessive combination of time of exposure plus the milliamperage load on the tube:

Still another object of the invention is to prevent any excessive combination of time; kilovoltage or milliamperage so as to overload the tube to-the point of injury.

Another object of the present invention is to provide control means preventing overloading of the X-ray tube by an excessive combination of kilovoltage together with a second control factor which includes theproduct ofthe milliamperage load on the; X-ray tube=times the numberof-seconds'the tube-is energized.

Qther objects and. advantages of the present invention will be-apparent from the accompanyingdrawings and description and the essential features -tl'iereof'wil1 be set forth in the appended- -claiinsw Ii-r the drawings, g

lis an electrical wiring diagram illustrating one formoiour device; -Fig;'--2--is--a wiring diagram showing a modified form of. our device.

AnX-raytube will take a definite maximum leading which-is a function-oi the milliamperage, the .kilovol-tage and the time for a definite load limit. If any one of the above is increased, then it'z-is necessary to decrease at least one of the othentwo: factors;

J In Fignl we have shown an autoi transformer ilflfisupplied with electrical energy from the cir cuitlLl, L2. Suitable taps connect leads II and 12 with the primary Isa of a high tension transfiormer- 13. ,The secondary [3b of this transformer,: is connected by leads I4 and 5- with the ;X-raytube 16 in the usual manner. The midportion of the secondary circuit of the transformer is-groundedat I! in the usual manner.

An exposure. is initiated in the customary mannerby closing-push button l8 which completes a circuit from L-lthrough linesl9 and 26 through the push button and. line 21 torelay 22 and then through lines 23 andfill rto the mid-point of the auto-transformer. This energizes relay i Claims. (01. 250-95) 2t 22 attracting the armature 22a; so that current flows through line l2 and normally closed arma ture 25b of relay 25th the primary [3b of the high tension transformer. The timing of the exposure is controlled by the space discharge tube 26 which is of the gasfilled triode type having a cold cathode 2611? a plate 261) and acontrol grid 26c. I-hepower supplyfor this tubeis providedfrom the circuit L3, L4 to the primary 21 eftran'sformer 2]; The secondary oif th'i s ransformer 21b provided with a ieotifier" tube 28- SO that rectified ul'reiit is supplied to the leads '29 anqi: 30'. The siresof the control grid Zfi df the timer-tubeincliides resistance 3|, condenser 3 2, and a time-selector switch 33 having a series" of v limiting resistors 33a; 33b, 33c and 33dl The connecting lines 34 and 36 are tapped intovariable resistance" 31 so as to apply the desired voltage on grid zse. Means is provided for shdrt-circuitiiig condenser 32 upto the mement that an exposureis'initiated. This comprises lines 38, 39 normally closed arrn'ature 22b of relay 22; andlines 46, 29- and. When relay 22 is energized to start an exposure, armature 22b opens this short circuit of the con;- denser. Then; the condenser begins to charge; the rate depending; among other things, upon the position of, the time selector s witch'; 3". As. soon as thevolt'age oi", condenser-{32 re c es a critical value there is abrea'kdown between the control grid :60 and the cathodeltm thus firing the tube 26. This immediately carries over to the circuit ofplate' 26-2) and acts througlithe plate circuit, presently described; to; energize relay 25 which opens the normally closedarrn'a ture zlihstopping tl'ie exposure I 7 It, is .a wellykhblwn,characteristic,of the type Qf tube shown at 26 thateth firingof such" a isdependent notpnly upon.the, vo1'tage or gnu 2%,,bu1i on the.-,. V01fage bLplat'e fibuals'o. In other words; there ,is 'anlintererelationship between the. voltage of. the .Igrid andhplate either ofwhichwill c,a us.e.,tlie, tube .to me. Wev make use of this characteristic of thetubetointrofdu'ce factors responsive to variations in the Kilovoltage andmillia npere load applied. to X-ray tube H5 in order to 'cohtrolth'evfiiiilig Qfl fllbe 26}. It, is Obviousl. that .our invention might be 'appl'iedto modify ,theiiring of tube 26 either. uuon. ,varia' tions oi "kflovoltage. alone or of ,m'ill'iamperage alone, but welpreferto a-pply corrections for both of these factors'at the samet'iine.

. In .thecircuit of. plate 26,11 are; linen 6133? 25-, line 43, secondary flar qf transfonner 14, line 45 and secondaryvllid oi transformer '46.

The transformer 44 provides a corrective factor responsive to variations in the kilovoltage applied to the X-ray tube. To this end, the primary 44b of the transformer 44 is connected across lines I] and 12 with the variable resistor 41 to set the desired current for the transformer primary 44b. Thus, as the kilovoltage controlled through lines ll and I2 varies up or down the current in the transformer secondary 44a will vary up or down in like manner, so as to provide a corrective factor in the circuit of plate 261). If the kilovoltage increases beyond a predetermined point, then the voltage on plate 2619 will increase and will fire tube 26 so as to terminate the exposure.

The corrective factor for milliamperage of X-ray tube 16 is applied in the plate circuit of tube 26 by means of the secondary 46a of transformer 46 as previously mentioned. The primary 46b of this transformer is in circuit with the filament transformer for the X-ray tube. This circuit includes lines 48 and 49, primary 50a of the filament transformer 50, line primary 48b of transformer 46 and line l9. Since the load on the X-ray tube is roughly proportional to the current supplied to the primary 50a of the filament transformer, the transformer 46 will be responsive to variations in the load on the X-ray tube, and through its secondary 46a will supply a corrective factor in the circuit controlling plate 26b. Thus, as the load on the X-ray tube increases, the voltage on plate 251) will increase and upon reaching a predetermined level will fire tube 26 and terminate the exposure.

To limit the filament current corresponding to the time selected at switch 33, a gang switch 52 is provided which is operated in unison with switch 33, such connection being indicated by the broken line 53. A shunt resistor 54 is provided across the transformer primary 461), the various taps of which are connected to similar taps 52a, 52b, 52c; 52d and 52a of the gang switch 52. Thus, corresponding to a definite time setting picked off by switch 33, a filament current limiting resistor is picked off by switch 52 which governs the amount of voltage to be introduced into the plate circuit of the timer tube 26.

-The transformers 44 and 46 are so constructed and adjustable resistances so selected, that the voltages introduced by them into the circuit of plate 26?) cause the tube 26 to fire whenever excessive kilovoltage or milliamperage, or a combination of both, is introduced into the X-ray tube control circuits, always in correspondence to the time of tube exposure.

It should be noted that the compensating voltages in the control circuit for tube 26 are always on, even though an exposure is not initiated. Therefore, tube 26 may fire and open relay at the armature 25b thereof before push button I8 is closed, in an attempt to start the exposure. This means that should the factors for the exposure be chosen so as to impose too great a load upon the X-ray tube, then it would be impossible to start an exposure.

Preferably, we provide an indicating device 55, such as a lamp or the like, to show that relay 25 is open and that the exposure chosen would impose too great a load upon the X-ray tube. To this end, lamp 55 is in circuit with lines 24, 48, 56, 51 and [5 when relay armature 25a is attracted by the energization of relay 25.

Fig. 2 shows a modification of Fig. 1 wherein similar parts having similar functions have been given the same reference characters and only the differences will be explained here. The purpose of Fig. 2 is to provide a correction factor which more directly is responsive to the milliamperage applied to the X-ray tube l6. For this purpose, the correction factor for the load on the X-ray tube is supplied through transformer 58, whose secondary 58a occupies the same place in the eontrol circuit of plate 26?) as that occupied by the transformer secondary 46a previously described. The primary 58b of this transformer is connected by lines 59 and 60 in the central secondary circuit of high tension transformer 13. Here, as in the previously described modification, the shunt resistor 54 is connected to suitable taps on gang switch 52 so that a definite load factor permissible on the X-ray tube is selected with each movement of the timer switch 33. In this modification, the filament transformer 6| has a primary Bla connected with the source L5, L6, in any suitable manner, as the filament transformer is not directly concerned in the safety control circuit in this modification of our device.

All of the other factors of Fig. 2 correspond to those described in Fig. 1 and any change in kilovoltage or load applied to the X-ray tube provides a corresponding variation in the firing of tube 26 which opens the relay 25b of relay 25 to terminate the exposure. The armature 25a and the indicating lamp 55 have been omitted from Fig. 2, but obviously, they may be used as shown in Fig. 1, if desired.

In Figs. 1 and 2, we have shown the autotransformer [8 with energizing circuit Ll, L2, and a self-rectified unit. However, those skilled in this art will recognize that in most cases the type of X-ray unit used would be provided with a four-valve-bridge-circuit. Our invention may be used, however, using either a self-rectified circuit, a half-wave rectified circuit, or a fullwave rectified bridge circuit, as will be readily understood.

What we claim is:

1. In the combination of an X-ray tube having a high tension tube energizing circuit and a filament energizing circuit including a fila ment transformer having primary and secondary windings, switch means controlling energi zation of said X-ray tube, a space discharge tube operatively connected with said switch means, said space discharge tube having control electrode means, a variable resistance timing means in circuit with said control electrode means, a control transformer having a primary winding in series circuit with said filament transformer primary winding and having a secondary winding, and said control transformer secondary winding in electrical circuit with said control electrode means and varying the voltage applied to the latter.

2. In the combination of an X-ray tube hav ing a high tension tube energizing circuit including a high tension transformer having primary and secondary windings and including a filament energizing circuit having a filament transformer with primary and secondary windings, means controlling energization of said X-ray tube including a space discharge tube having control electrode means, timing means for selecting a variable resistance, a first control transformer having a primary winding in circuit with said high tension transformer primary winding, a second control transformer having a primary winding in circuit with said filament transformer primary winding, each of said control transformers having a secondary winding, and said secondary windings ofsaid control transformers and said variable resistance in electrical circuit with said control electrode means.

3. In the combination of an X-ray tube having a high tension tube energizing circuit including a high tension transformer having a primary winding and having a secondary winding with a central secondary grounded circuit, means controlling energization of said X-ray tube including a space discharge tube having control electrode means, timing means for selecting a variable resistance, a control transformer having a primary winding in said central secondary grounded circuit and having a secondary winding, and said control transformer secondary winding and said variable resistance in electrical circuit with said control electrode means.

4. In the combination of an X-ray tube having a high tension tube energizing circuit including a high tension transformer having a primary winding and having a secondary winding including a central secondary grounded circuit, means controlling energization of said X-ray tube including a space discharge tube having control electrode means, timing means for selecting a variable resistance, a first control transformer having a primary winding in circuit with said high tension transformer primary winding,

a second control transformer having a primary winding in said central secondary grounded circuit, both of said controi transformers having secondary windings, and said control transformer secondary windings and said variable resistance in electrical circuit with said control electrode means.

EDWIN R. GOLDFIELD.

JACK BALL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name 1 Date 2,053,587 Van Den Berg Sept. 8, 1936 2,339,902 Akers et-al. Jan. 25, 1944 2,379,125 Weisglass June 26, 1945 2,404,905 Garretson July 30, 1946 FOREIGN PATENTS Number Country Date 517,349 Great Britain Jan. 26, 1940 547,030 Great Britain Aug. 11, 1942 552,945 Great Britain Apr. 30, 1943 

